The present invention relates to an information embedding method, and apparatus. In particular, the present invention relates to a method, and apparatus, for embedding information such as copy control information and copyright information in digitized contents information of a still picture or moving picture, and to a program medium for implementing the method.
In recent years, contents of images and music have been digitized and circulated via storage media or communication networks. In order to protect the copyright of such digitized contents information, a digital watermark technique is regarded as important. In this digital watermark technique, copy control information and copyright information are embedded in contents information by making a change of such a degree as not to be noticed by human visual and auditory senses in the contents information. As a result, it is possible to limit the number of times of copy of contents information utilizing data processing apparatuses or specify the copyright holder on the basis of illegally copied contents information.
For putting the digital watermark technique to practical use, it is necessary to satisfy the following two requirements.
(1) Suppression of degradation of contents information:
For example, in embedding digital watermark information in image data, a change made in image must not prevent enjoyment of contents. In other words, a change made in a part of contents information must not be conspicuous to human visual and auditory senses.
(2) Improvement of survivability:
Even if image processing and voice processing are applied, embedded information, i.e., a change made in contents information must not be easily degraded.
For satisfying the above described conditions, it is necessary to optimize change positions and degrees or intensities of changes in contents according to the property of the contents. By taking an image which is representative of contents information, as an example, conventional digital watermark techniques will hereafter be analyzed.
In the case of image data, making an unsuitable change in a state value (luminance or color) of a pixel in such an area that the state change of an image is comparatively flat typically causes conspicuous unnaturalness in the changed position. However, a portion where a pixel value variation is violent, such as an edge portion of a subject, has a property that a comparatively large change made in pixels is not conspicuous to human eyes. Paying attention to this property, a digital watermark technique of edge preservation type has been proposed in, for example, The Transactions of the Information Processing Society of Japan, Vol. 38, No. 12, 1997, pp. 2640-2647. In this technique, an edge portion of a subject is identified by analyzing the luminance variation of an image frame in which watermark information should be embedded. In the above described edge portion where a pixel value change is hard to be conspicuous, a large change is made. In a portion where a pixel value change is easy to be conspicuous, a change is not made, or the degree of a change is made low even if the change is made.
The subject of embedding of digital watermark information is not limited to still pictures, but moving pictures also become the subject. Moving picture data is formed of a plurality of still picture frames arranged in time series. In some cases, the frame feed is stopped during enjoyment of a moving picture to enjoy individual frames as still pictures.
In embedding digital watermark information in a moving picture, it is necessary to make pixel value change positions inconspicuous in both the still picture state and the moving picture state, for the above described reason. Therefore, it is desirable to optimize pixels to be changed and the degree of the change by considering both the property as viewed as a still picture and the property as viewed as a moving picture. As for conventional techniques concerning embedding digital watermark information in a moving picture, however, only the property as viewed as a still picture is considered in, for example, a system reported in 1997 Symposium on Cryptography and Information Security, 31-G. On the other hand, in a system reported in 1997 Symposium on Cryptography and Information Security, 31-F, only the property as viewed as a moving picture is considered. There has not been proposed yet an example in which pixel value change positions and/or change intensities are optimized by considering both the property as viewed as a still picture and the property as viewed as a moving picture.
Furthermore, conspicuousness of a pixel value change does not depend upon only one property such as, for example, a luminance variation, but differs according to a property other than luminance such as a color variation. When embedding watermark information in a still picture or a moving picture, therefore, it is necessary to optimize change positions and degrees of the change, i.e., change intensities while considering these plural properties. In conventional digital watermark techniques, however, the pixel value change is optimized depending upon one property of an image. An optimization technique considering a plurality of properties has been neither proposed nor well known.
A first object of the present invention is to provide a technique of optimizing change positions i.e., change positions and/or change intensities on the basis of a plurality of properties possessed by contents information in which watermark information should be embedded.
A second object of the present invention is to provide a method, and apparatus, for embedding watermark information in a moving picture optimized in change position and/or change intensities on the basis of both the property as viewed as a moving picture and the property as viewed as a still picture.
Another object of the present invention is to provide a computer program for implementing the above described information embedding method, and contents information obtained by implementing the method.
In order to achieve the above described first object, an information embedding method according to an aspect of the present invention includes a step of determining a plurality of change positions and/or change degrees of states respectively depending upon a plurality of properties possessed by contents information serving as an embedding subject of watermark information, a step of selecting change positions and/or change degrees to be applied to each of sub-contents information pieces representing divisional contents information according to the contents information, among the plurality of change positions and/or change degrees determined on the basis of the respective properties, and a step of making a change serving as watermark information in the contents information in accordance with the selected change positions and/or change degrees.
In a more concrete aspect, the information embedding method includes the steps of dividing contents information serving as an embedding subject of watermark information into a plurality of information blocks, determining change positions and/or change degrees for the information blocks, and for each of information blocks, selecting at least one among the determined change positions and/or change degrees according to contents information of the information block.
If priority is given to inconspicuousness of the change, then, for example, a result of a logical product (AND) operation conducted on change positions and/or change degrees selected for respective properties may be used as final change positions and/or change degrees at the selection step so as to minimize the number of change positions and/or change degrees. On the other hand, if priority is given to survivability of the change result, than a result of a logical sum (OR) operation conducted on change positions and/or change degrees selected for respective properties may be used as final change positions and/or change degrees at the selection step so as to maximize the number of change positions and/or change degrees.
In order to achieve the above described first object, an information embedding method according to another aspect of the present invention includes a first step of determining change positions and/or change degrees of states on the basis of a first property possessed by contents information serving as an embedding subject of watermark information, a second step of amending at least a part of change positions and/or change degrees determined at the first step, on the basis of a second property possessed by contents information different from the first property, and a third step of making a change serving as watermark information in the contents information according to the amended change positions and/or change degrees.
In order to achieve the above described first object, an information embedding method according to still another aspect of the present invention includes a first step of selecting at least one among a plurality of rules prepared beforehand, on the basis of a first property possessed by contents information serving as an embedding subject of watermark information, a second step of determining change position and/or change degree candidates of the contents information on the basis of a second property possessed by contents information, a third step of determining at least one change position and/or change degree out of the change position and/or change degree candidates, based upon a rule selected at the first step, and a fourth step of changing a state of the contents information in the selected change position and/or change degree.
In accordance with the present invention, each of the above described plurality of rules is provided with a content for prescribing change positions and/or change degrees according to one property of the contents information. By applying one rule selected on the basis of another property of the contents information, change positions and/or change degree can be determined in such a form as to take a plurality of properties possessed by the contents information into consideration.
In order to achieve the above described second object, in accordance with an aspect of the present invention, an information embedding method of embedding watermark information by making a change in moving picture data formed of a plurality of still picture frames includes a first step of determining change positions and/or change degrees on the basis of a property as viewed as a still picture, detected from a still picture frame to be processed, a second step of determining change position candidates and/or change degree candidates on the basis of a property as viewed as a moving picture, detected from a relation between images contained in the still picture frame to be processed and another still picture frame, a third step of selecting change positions and/or change degrees to be applied to the still picture frame among the change position candidates and/or change degree candidates respectively determined at the first and second steps, and a fourth step of making a pixel change serving as watermark information in the still picture frame to be processed in accordance with the selected set of change positions and/or change degrees.
In order to achieve the above described second object, in accordance with another aspect of the present invention, an information embedding method of embedding watermark information by making a change in moving picture data formed of a plurality of still picture frames includes a first step of determining change positions and/or change degrees on the basis of a property as viewed as a still picture, possessed by each of the still picture frames, a second step of modifying at least a part of the change positions and/or change degrees determined at the first step, on the basis of a property as viewed as a moving picture, determined from a relation between the still picture frames, and a third step of making a pixel change serving as watermark information in the still picture frame in accordance with the modified change positions and/or change degrees.
In order to achieve the above described second object, in accordance with still another aspect of the present invention, an information embedding method of embedding watermark information by making a change in moving picture data formed of a plurality of still picture frames includes a first step of selecting one among a plurality of rules prepared beforehand, on the basis of a property as viewed as a moving picture, detected from a relation between images contained in the still picture frame to be processed and another still picture frame, a second step of determining change positions and/or change degrees in the still picture frame on the basis of a property as viewed as a still picture, detected from the still picture frame to be processed, using the determined rule, and a third step of changing a pixel state of the still picture frame in the selected change position and/or change degree.
In a more concrete aspect of the foregoing aspects, each of the still picture frames is divided into a plurality of image blocks, and the above described series of processing steps are executed for each image block. As the property as viewed as a still picture, for example, a luminance variation in each still picture frame or in each image block may be considered. As the property as viewed as a moving picture, a motion quantity, i.e., the magnitude of a motion vector between still picture frames may be considered.
An information embedding apparatus according to the present invention includes a processor for executing the above described steps by means of program processing, and a storage device for storing contents information to be processed and other data. Its specific configuration will become clear by embodiments described hereafter.